The present invention relates to a surface mount assembly for electronic components and, more particularly, to a surface mount assembly for electronic components with the supply of solder paste by using a screen printing.
Conventional methods of mounting electronic components on a substrate involve placing a metal mask on a smooth, flat surface of the substrate. Solder paste is screened into openings in the metal mask as solder portions for the subsequent mounting of electronic components on the substrate. Some of the electronic components require a relatively large amount of solder paste while others don't. In the case that the electronic components require the large amount of solder paste, the solder portions are required to have a relatively large size in thickness. However, the screen printing conventionally used is not adapted to supply different amounts of solder paste for different components.
Japanese Patent Laid-Open No. 62-181494 discloses a method of mounting electronic components on a substrate that overcomes the above-mentioned problem. This method employs two masks: a first mask having large windows for supplying a larger amount of solder paste as well as small windows for a smaller amount of solder paste and a second mask having large windows for supplying a larger amount of solder paste. The solder paste is supplied onto the substrate by using the first mask and then the second mask overlapped with the first mask on the top surface thereof. This approach is hereinafter referred to as a first prior art.
There is another method that overcomes the above-mentioned problem in which a plurality of openings are formed in a metal mask for screen printing at the position corresponding to the electronic components to be mounted on a substrate. The openings are varied in diameter for supplying different amounts of solder paste to the substrate for the different electronic components. This approach is hereinafter referred to as a second prior art.
The first prior art requires two or more masks depending on the desired amount of the solder paste for the different electronic components. On the other hand, the second prior art requires the metal mask to have a uniform thickness because the amount of the solder paste to be supplied on the substrate is determined according to the difference in diameter. Thus, the amount of the solder paste in the openings would be suitable for one or some of the electronic components and may not be good for the remainders. Since solder paste spread away in the openings, the difference in diameter is not a sufficient factor for precise control of the amount of the solder paste in the openings.
Furthermore, since conventional substrates have a uniform thickness, a connector cannot be attached to a side of the substrate when the thickness exceeds a certain limit.